This invention relates in general to electromagnetic coordinate switching devices and more particularly to those of the type including a magnetic shunt plate or plates, an array of magnetically responsive switching elements inserted in said shunt plate in rows and columns at respective points of intersection of row and column signal lines extended substantially at right angles, and excitation coils or windings applied to the switching elements. As is well known, this type of electromagnetic coordinate switching device is well suited for use as a speech-path switching network in an automatic telephone exchange, a hybrid electronic computer or the like apparatus, and the present invention is particularly concerned with improvements in construction of the type of coordinate switching device.
Electromagnetic coordinate switches of the general type including switching elements arranged in rows and columns are known in the prior art as exemplified by a technical article entitled "The Ferreed" and published in the Bell System Technical Journal, Vol. 43, No. 1 (January 1964). As disclosed therein, each of the switching elements used includes a hollow dielectric spool molded into a shunt plate and extending on both sides therefrom at right angles thereto, at least one reed switch and magnetic core means disposed within the spool, and a plurality of pairs of windings wound around the spool on the top and bottom sides of the shunt plate. In this form the spools of the switching elements in each row and column must be spaced sufficiently from each other to permit a winding bit, in forming each of the windings on the individual spools, to pass freely around the latter without damaging adjacent windings. In space division electronic switching systems, coordinate switches, which provide for the selection of speech paths, constitute about sixty percent of the whole apparatus. Therefore, not only are the magnetic switches important in the functioning of the system but their bulk, weight and cost are critical factors in the economy of the entire switching system.
As described above, the excitation coils are conventionally formed on each of the spools mounted on the shunt plate, making it difficult to reduce the spacing between switching elements in attempting to reduce the size of the coordinate switch. Under this situation, formation of windings having any increased number of turns on the individual spools is troublesome and hardly practicable because the separate spool configuration involves a substantial increase in winding time and hence in fabrication cost of the switching device. However, it is desirable to increase the number of turns of the windings because this allows a reduction in the driving power required to operate the switches. It has further been found that it is extremely difficult to decrease the magnitude of driving current while using high-speed solid state circuits for the driving of such electro-magnetic coordinate switching device.
To cope with these difficulties, a coordinate switching device, including improvements in coil configuration and in aligned formation of crosspoints, has been proposed in the U.S. Pat. No. 3,487,344 issued to Takamura et al. on Dec. 30, 1969. Here sets of crosspoints, each including a plurality of crosspoint elements, are fixedly arranged on respective elongate magnetic shunt plates and are wrapped with primary windings. The shunt plates are arranged parallel to each other to form respective columns of crosspoints and thereafter, secondary windings are applied to the respective rows of crosspoints, each surrounding all the crosspoints in the associated row as a winding common to such crosspoints.
Further, with this arrangement, featuring a segmental array formation and secondary windings common to respective rows of crosspoints, since selection of the crosspoints is effected by coincidence of the direction logic of magnetic fields applied, as will be described later, two sets of excitation coils arranged in rows and columns are energized at the same time to produce a magnetomotive force of substantial magnitude as required for the closing of a switching element selected. This involves a material rise in coil impedance, having a tendency to cause increase the magnitude of the driving power required for the operation of the system.
Further with this arrangement, when only excitation coils associated with row control lines or with column control lines are energized, all the switching elements are opened. Accordingly, when a switching element at any crosspoint is operated to close, the switching elements in the same row and column are all automatically opened and this makes multiple connection of the switching elements in any particular row or column impossible.
Moreover, in previous forms of coordinate switching device, cores of semihard magnetic material are required at the respective crosspoints as means for magnetically holding the switching elements and fitted in the coil spools. Insertion of the cores in the respective coil spools, however, can hardly be automated as the cores must be combined preliminarily with the respective associated switching elements. A further difficulty encountered in the prior art is that the wrapping connection of input and output lines to the coordinate switching device has made its maintenance rather difficult.